David,
If your going to start with the Sport Pilot License, then you have to answer the following economic questions:
Can you rent and fly a LSA aircraft locally and at what cost?
If you can't rent one then you need to consider moving up to the Private License which would allow you to rent or buy a whole lot of aircraft. This is a cost comparison problem equal to a "mission" question.
If I correctly read the proposal that opens this thread, then you need a Private License in order to qualify for the proposed waiver. That being the case, the next question is are you going for the Sport ticket to save $ and get started or do you need the medical exemption in order to fly anything?
I think from a pure cost standpoint the Sport License is the cheapest way to start flying and if you can get that license in an old tail dragger you will learn basic airmanship better than in a trike trainer. Even if you plan on flying a trike LSA in the future I would recommend you start in a tail wheel aircraft. This advice is given by a guy who trained in a C-150 a long time ago (1992). The cost to upgrade from Sport Pilot to Private is roughly the same as the cost to obtain the Sport Pilot ticket, you need a total of 40 hours and you'll have about half of that when you get the Sport ticket. If your doing the Sport pilot training at a towered airport then you will have a "leg-up" since you'll get the basic radio training you'll need for the Private. At this point in time the PPL 3rd class medical waiver is only a proposal and it's been kicked around aviation blogs for the past year, so don't count on anything coming out of the FAA real soon.
Good Luck and have fun with the Sport Pilot training!,
Joe